Document Type: Original Research Paper


Department of Electrical Engineering, Faculty of Technical and Vocational No.2, Kermanshah Branch, Technical and Vocational University (TVU), Kermanshah, Iran.


Background and Objectives: In this paper, an ultra-wide stopband microstrip low pass filter (LPF) with sharp roll-off and compact size is designed and fabricated. Also, proposed filter is designed, simulated, optimized, fabricated and measured and we can see a good agreement between the simulations and measurement results.
Methods: T-shaped and stepped impedance have been used, because these structures have a very small dimensions. This method provides a suitable cut off frequency.
Results: The cut off frequency at -3dB is 3.1GHz. In the proposed structure, the insertion loss is lower than 0.12dB and the return loss is greater than 15dB. In order to achieve a -20dB attenuation level in the stopband, a modified L-shaped structure is utilized.  This filter has an ultra-wide stopband that is expanded from 3.37GHz to 37.5GHz. Also, the suppression level is greater than -20dB. The fabricated LPF has a size about 16.6 × 13.5 mm2 which is equal to 0.28ƛg × 0.22ƛg, where ƛg is the guided wavelength at 3.1GHz, which is very small.
Conclusion: A microstrip LPF with 3.1GHz cut-off frequency consisting of T-shaped and stepped impedance resonators has been proposed, simulated and fabricated. The transition band (-3 to -40dB) is 0.38GHz, which is a very sharp response. The stopband of the proposed filter is from 3.37 to 37.5 GHz which is equal to 12.1fc. There was a significant agreement between the simulation and the measured results. With all these features, these filters are widely used in wireless communication systems.


Main Subjects

[1]   D. M. Pozar, Microwave Engineering, Wiley, New York, 2005.

[2]   J. S. Hong and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications. New York: Wiley, 2001.

[3]   M. Hayati, F. Shama, and H. Abbasi, “Compact microstrip lowpass filter with wide stopband and sharp roll-off using tapered resonator,” International Journal of Electronics, vol. 100, no. 12, pp. 1751-1759, 2013.

[4]   S. Jiang and J. Xu, “Compact microstrip lowpass filter with ultra-wide stopband based on dual-plane structure,” Electronics Letters, vol. 53, no. 9, pp. 607-609, 2017

[5]   P. M. Raphika, P. Abdulla, and P. M. Jasmine, “Planar elliptic function lowpass filter with sharp roll-off and wide stopband,” Microwave and Optical Technology Letters, vol. 58, no. 1, pp. 133-136, 2016.

[6]   F. Wei, L. Chen, and X. W. Shi, “Compact lowpass filter based on coupled-line hairpin unit,” Electronics Letters, vol. 48, no. 7, pp. 379-381, 2012.

[7]   M. Hayati, M. Ekhteraei, and F. Shama, “Compact lowpass filter with flat group delay using lattice-shaped resonator,” Electronics Letters, vol. 53, no. 7, pp. 475 – 476, 2017.

[8]   A. Sheikhi, A.  Alipour, and H. Hemesi, “Design of microstrip wide stopband lowpass filter with lumped equivalent circuit,” Electronics Letters, vol. 53, no. 21, pp. 1416-1418, 2017.

[9]   L. Kumar and M. S. Parihar, “Compact hexagonal shape elliptical lowpass filter with wide stop band,” IEEE Microwave and Wireless Components Letters, vol. 26, no. 12, pp. 978-980, 2016.

[10]   H. Sariri, Z. Rahmani, A. Lalbakhsh, and S. Majidifar, “Compact LPF using T-shaped resonator,” Frequenz, vol. 67, no. 1–2, pp. 17–20, 2013.

[11]   V. K. Velidi and S. Sanyal, “Sharp roll-off lowpassfilter with wide stopband using stub-loaded coupled-line hairpin unit,” IEEE Microwave and Wireless Components Letters, vol. 21, no. 6, pp. 301–303, 2011.

[12]   A. Faraghi, M. Ojaroudi, N. Ghadimi, “Compact microstrip low-pass filterwith sharp selection characteristics using triple novel defected structures for UWB applications,” Microw. Opt. Technol. Lett., vol. 56, no. 4, pp. 1007–1010, 2014.

[13]   X. Chen, L. Zhang, Y. Peng, Y. Leng, and H. Lu, Z. Zheng,  “Compact lowpass filter with wide stopband bandwidth,” Microw.Opt. Technol. Lett., vol. 57, no. 2, pp. 367–371, 2015.

[14]   P. M. Raphika, P. Abdulla, and P. M. Jasmine, “Compact lowpass filter with a sharproll-off using patch resonators,” Microw. Opt. Technol. Lett., vol. 56, no. 11, pp. 2534–2536, 2014.

[15]  H. L. Cao, W. B. Ying, and H. Li, S. Z. Yang, “Compact lowpass filter with ultra-wide stopband rejection using meandered-slot dumbbell resonator,” J. Electromagn. Waves Appl., vol. 26, no. 17-18, pp. 2203– 2210, 2012.